In plants comprising screw compressors, in particular in refrigerating plants, as shown, for example, in DE 10 2005 018 602 A1, non-return valves are usually disposed on the suction side of the compressors in order to prevent a rearward rotation of the compressor as a result of the pressure difference before and behind the compressor when the compressor drive is switched off, which rearward rotation could damage said compressor. Such non-return valves likewise serve to ensure that, when the compressor is at rest, the pressures of the plant before and behind the compressor do not equalize.
Such plants usually possess filters on the suction side of the compressors in order to prevent dirt from penetrating the compressor and damaging it.
In smaller and medium-sized compressors (up to about 800 m3/h suction volume), non-return valves integrated in the compressor housing, which are opened by the gas stream and closed by a compression spring, are customary. DE 10 2006 016 317 A1 shows an exemplary design which is actuated by a compression spring. In such compressors, suction gas filters integrated in the compressor housing are likewise customary.
Plants comprising larger compressors often have non-return valves and suction gas filters as separate components. The closure of the non-return valves is here advantageously realized not by a compression spring, but by gas which is under final pressure of the compressor, as described in patent application DE 10 2013 010 780.6. In order to provide the gas, plant components after the compressor are connected by pipelines, and a solenoid valve contained therein, to the non-return valve, which is disposed before the compressor. Valves of this construction have lower flow losses than valves having a compression spring.
Because of their large flow losses, the non-return valves which are usually used in small compressors and which are actuated by a compression spring are not advantageous. The flow-favorable non-return valves which are actuated by pressurized gas and which are customary in plants comprising larger compressors are expensive. The separately disposed components require a plurality of housings connected by connecting elements, which leads to high complexity of machining and assembly. Pipelines are necessary to conduct gas from the pressure side of the compressors to the non-return valve, the threaded joints of which pipelines are often, in practice, the cause of gas leaks.